Surface Engineering Handbook

Author: Chief Editor: Li Guoying
Publisher:
Publishing Date: 2004-01-01
Features: The "Surface Engineering Handbook" was compiled by more than 50 experts and professors from across the country, invited by China Machine Press to meet the demands of. The handbook was edited by Sun Dazong, Executive Vice President of the China Association for Science and Technology (Professor-level Senior Engineer), and Preface was written by Xu Binshi, Academician of the Chinese Academy of Engineering. Li Guoying, Professor-level Senior Engineer of the Wuhan Institute of Materials Protection, Ministry of Machinery Industry, served as the Chief Editor. The handbook consists of 11 parts and 74 chapters, covering topics such as Introduction, Surface Finishing and Cleaning, Organic Coating, Thermal Spraying (Welding), Rust Prevention and Packaging, Chemical Heat Treatment, Vapor Deposition, High-Energy Beams (Laser, Electron, and Ion Beams), Electroplating, Conversion Film Technology, Surface Coating (Film) Quality Testing Technology, Corrosion Protection and Protective Engineering Design, and Industrial Applications of Surface Engineering Technology in Friction. Appendices list the current surface engineering-related standards in China. It is a reference for engineering technicians, managers, and faculty and students from universities and colleges in the fields of machinery, materials, chemical engineering, metallurgy, shipping, railways, and aerospace.
Excerpt: Fats and oils are not soluble in water but can be made soluble in water after saponification, allowing them to be removed from the surface being treated. Non-saponifiable oils—mineral oils that do not react chemically with alkalis, such as lubricating oils and petroleum jelly—can be converted into emulsions and removed by adding surfactants like sodium silicate, especially surfactants such as OP emulsifiers. Common materials used to prepare alkaline cleaning solutions include the following:
(1) Sodium Hydroxide (NaOH), also known as caustic soda, is a strong alkali that primarily saponifies animal and vegetable oils but requires heating. It has a corrosive effect on non-ferrous metals and poor water-washability (i.e., it is not easily rinsed clean).
(2) Sodium Carbonate (Na?CO?), also called soda ash, can saponify and soften water, maintaining a certain alkalinity in the solution. It has lower alkalinity and corrosiveness to non-ferrous metals compared to sodium hydroxide, but its water-washability is also poor.
(3) Sodium Tripolyphosphate (Na?PO?) has good buffering properties, with a 0.5% aqueous solution having a pH of 11.8. It has a certain surface activity, capable of emulsifying and dispersing oil, and provides corrosion inhibition for metals. This material can also be replaced by other phosphates such as sodium dihydrogen phosphate, sodium tripolyphosphate, and sodium pyrophosphate.
(4) Sodium Silicate (Na?SiO?), commonly known as water glass or soda ash. It is composed of Na?O and SiO?, with the general formula mNa?O·nSiO?, where m/n is the modulus. The properties of water glass change with the modulus; a higher n value results in a lower modulus and stronger alkalinity. Water glasses with a modulus of 1:1 to 1:3 are commonly used for degreasing. Water glass has surface activity, capable of emulsifying and dispersing mineral oils, and provides corrosion inhibition for metals. In degreasing solutions, the concentration of alkaline salts, especially sodium hydroxide, should not be too high, as this would reduce the solubility of soap and the stability of the emulsion formed, while also causing corrosion to non-ferrous metals. Therefore, different materials and ratios should be selected for different treatment processes and materials.
2.2 Alkaline Cleaning Solution Formulations
Alkaline cleaning solutions come in many types, with similar components. Some typical formulations, process conditions, and applications are shown in Table 1.2-1. The formulation and process conditions for electrolytic degreasing solutions are the same as those for chemical degreasing solutions, except that the concentration is slightly lower. The formulations and process conditions are shown in Table 1.2-2.
3 Alkaline Cleaning Process Methods
3.1 Classification and Main Characteristics of Process Methods
Alkaline cleaning processes are classified into three types based on their operational methods: immersion, spraying, and tumbling.
(1) Immersion Method: Workpieces are immersed in a specified concentration and temperature of alkaline cleaning solution until all oil is removed. This is currently the most widely used degreasing method and can be further divided into ordinary immersion, electrolytic, and ultrasonic methods.
① Ordinary Immersion Method: Workpieces are placed in a certain temperature and concentration of alkaline cleaning solution, where the oil is removed through saponification and emulsification of the alkaline solution. This method has simple equipment and convenient operation and is suitable for complex-shaped workpieces. Immersion methods are divided into fixed and through types. Fixed-type tanks are equipped with agitating systems, while through-type workpieces move themselves. Both types can improve degreasing efficiency. The equipment is shown in Figure 1.2-1.